3GPP (3rd Generation Partnership Project) is a project for discussing and preparing specifications of cellular telephone systems based on networks of evolved W-CDMA (Wideband-Code Division Multiple Access) and GSM (Global System for Mobile Communications). In 3GPP, the W-CDMA system has been standardized as the 3rd-generation cellular mobile communication system, and its service is started sequentially. Further, HSDPA (High-Speed Downlink Packet Access) with further increased communication rates has also been standardized, and its service is started. 3GPP is discussing evolution of the 3rd-generation radio access technique (Evolved Universal Terrestrial Radio Access: hereinafter, referred to as “E-UTRA”).
As a downlink communication system in E-UTRA, proposed is an OFDMA (Orthogonal Frequency Division Multiple Access) system for multiplexing users using mutually orthogonal subcarriers. Further, in the OFDMA system are applied techniques such as an adaptive modulation/demodulation-error correcting scheme (AMCS: Adaptive Modulation and Coding Scheme) based on adaptive radio link control such as channel coding, etc.
AMCS is a scheme for switching radio transmission parameters such as a coding rate of error correction, the level of data modulation, etc. corresponding to propagation path conditions of each mobile station apparatus so as to efficiently perform high-speed packet data transmission. For example, data modulation is switched to a multilevel modulation scheme with higher modulation efficiency such 16 QAM (Quadrature Amplitude Modulation), 64 QAM, etc. from QPSK (Quadrature Phase Shift Keying) as the propagation path conditions are better, and it is thereby possible to increase maximum throughput in the mobile communication system.
In OFDMA, it is possible to physically divide the communicable region in the frequency domain corresponding to subcarriers and time domain. A combination of some divided regions is referred to as a resource block, one or more resource blocks are allocated to each mobile station apparatus, and communications are performed while multiplexing a plurality of mobile station apparatuses.
In order that the base station apparatus and each mobile station apparatus perform communications with optimal quality and rate in response to the request, required is resource block allocation and transmission scheme determination with consideration given to the reception quality in each subcarrier in the mobile station apparatus. Since the base station apparatus determines the transmission scheme and scheduling, and only the mobile station apparatus knows downlink propagation path conditions in Frequency Division Duplex, to achieve the request, each mobile station apparatus is required to give feedback of reception quality (corresponding to MCS (Modulation-Error correcting coding scheme) receivable in the mobile station) to base station apparatus. The reception quality of each mobile station apparatus is fed back to the base station apparatus by using CQI (Channel Quality Indicator).
Further, to increase the communication path capacity in E-UTRA, the use of transmission diversity has been proposed such as SM (Space Multiplexing) technique using MIMO (Multiple Input Multiple Output), SFBC (Space-Frequency Block Code) and the like. By using MIMO, it is possible to form a plurality of propagation paths as a space due to the effect of multipath, and multiplex a plurality of pieces of information to transmit. On the reception side, it is possible to combine power of a plurality of transmission antennas to obtain the reception gain. Herein, these techniques are collectively referred to as MIMO. In E-UTRA, it is assumed to use SM by MIMO and transmission diversity on downlink, and the scheme to perform communications is determined in consideration of propagation path conditions between the base station apparatus and mobile station apparatus.
In using MIMO-SM, to facilitate separation processing of a plurality of space multiplexed sequences transmitted from antennas, it is considered that the base station apparatus beforehand performs preprocessing on transmission signal sequences. The information of the transmission signal preprocessing cannot be calculated in the base station apparatus, and each mobile station apparatus needs to transmit the transmission signal preprocessing information to the base station apparatus as feedback in MIMO-SM communication.
Further, in MIMO-SM, the information of the number of spatially multiplexed signal sequences is also dependent on the propagation path between the mobile station apparatus and base station apparatus, and is calculated in the mobile station apparatus based on a reference signal transmitted from the base station apparatus. In other words, each mobile station apparatus needs to give feedback of this information to the base station apparatus as well as the above-mentioned feedback information.
As described above, to achieve MIMO-SM communication, each mobile station apparatus is required to transmit three kinds of information i.e. the reception quality information, transmission signal preprocessing information, and transmission signal number-of-sequence information as feedback for the communication path with the base station apparatus. The number of bits, format and transmission frequency required to give each feedback are different from one another, and are varied in a respective period corresponding to propagation path conditions and conditions of the mobile station apparatus.
More specifically, time variations are more moderate in the optimal number of sequences of transmission signals than in the transmission signal preprocessing information. When scheduling is performed to always concurrently transmit the optimal number of sequences of transmission signals and the transmission signal preprocessing information, and feedback is performed in accordance with the transmission period of the transmission signal preprocessing information, the number of sequences of transmission signals that is not varied undergoes feedback many times, and as a result, overhead arises in uplink resources. Meanwhile, when feedback is performed in accordance with the transmission period of the number of sequences of transmission signals, information of the transmission signal preprocessing information is insufficient in the base station apparatus. As a result, MIMO communication is performed by the preprocessing that is not suitable for the transmission signal, and system throughput decreases.
Further, the information amounts of the reception quality information and transmission signal preprocessing information are varied with the number of transmission signal sequences. More specifically, when different modulation schemes are applied for each transmission signal sequence, the reception quality information is required corresponding to the number of sequences. Further, the transmission signal preprocessing information is information represented by a matrix corresponding to the number of transmission signal sequences and the number of transmission antennas, and the number of required bits varies according to the number of transmission signal sequences. From such a feature, it is effective to transmit the number of transmission signal sequences fast among the above-mentioned feedback information, and to subsequently transmit the reception quality information and transmission signal preprocessing information corresponding to the reception quality information.
FIG. 11 contains a timing chart and sequence chart showing the flow of processing between the base station apparatus and mobile station apparatus in the conventional mobile communication system. An example as shown in FIG. 11 is to implement a mechanism as described in Non-patent Document to periodically transmit the reception quality information, transmission signal preprocessing information and the number of transmission signal sequences, is an example of transmitting each kind of feedback information on a periodically assigned uplink control channel (PUCCH: Physical Uplink Control Channel), and describes feedback of from subframes 1 to 16.
Herein, to simplify, omitted are downlink signals, uplink data signals, and feedback information such as ACK/NACK (Positive Acknowledgement/Negative Acknowledgement) transmitted to the base station apparatus from the mobile station apparatus, and the like. In this example, resources of the uplink control channel are allocated before subframe 1, and starting from subframe 1, resources are allocated every three subframes (710). For the reception quality information, transmission signal preprocessing information and the number of transmission signal sequences transmitted using the resources, their transmission timings are shown in “711”.
The base station apparatus notifies the mobile station apparatus of information about the number of times once which the number of transmission signal sequences is transmitted in the resources, and in this example, it is set that such information is transmitted once every four times in allocated resources. In other words, the number of transmission signal sequences is periodically transmitted in subframes 1 and 13, and it is assumed that the numbers of transmission signal sequences are “3” and “4” respectively (steps S701, S705). In remaining resources i.e. in subframes 4, 7, 10 and 16, the reception quality information and transmission signal preprocessing information is periodically transmitted (steps S702, 703, S704, S706).
At this point, the reception quality information and transmission signal preprocessing information is corresponding to the last transmitted number of transmission signal sequences. In other words, transmitted in subframes 4, 7 and 10 is the reception quality information and transmission signal preprocessing information corresponding to the number of transmission signal sequences transmitted in the subframe 1 i.e. “3”. Transmitted in a subframe 16 is the reception quality information and transmission signal preprocessing information corresponding to the number of transmission signal sequences transmitted in a subframe 13 i.e. “4”.
Meanwhile, in E-UTRA, to suppress power consumption in the mobile station apparatus, there is a technique of DRX (Discontinuous Reception) that the power is turned on only for the duration required by the mobile station apparatus to receive signals. FIG. 12 is a diagram showing the outline of DRX control. The mobile station apparatus repeats on-duration 802 and opportunity for DRX 803 in a DRX cycle 801 (repetition cycle). When the on-duration and DRX cycle are configured, the opportunity for DRX is uniquely determined. The on-duration is a period of time formed of one or more subframes defined to monitor PDCCH.
In the on-duration, the base station apparatus transmits PDCCH to start uplink or downlink resource allocation. A mobile station apparatus receiving PDCCH indicative of scheduling of uplink or downlink initial transmission data (new data) in the on-duration monitors PDCCH for a predetermined duration after the on-duration (804). Further, for a duration having the possibility of retransmission of uplink data or downlink data, the mobile station apparatus monitors PDCCH irrespective of whether the duration is in or out of the on-duration range (805). The duration is referred to as Active Time during which the receiving section of the mobile station apparatus is started and active to monitor PDCCH (806).
The base station apparatus transmits data during the Active Time of the mobile station apparatus. The base station apparatus beforehand notifies the mobile station apparatus of the repetition period and on-duration of the DRX cycle, and the mobile station apparatus beforehand repeats power-on periodically based on the information, while performing power-on corresponding to reception conditions of PDCCH and data retransmission conditions (see Non-patent Document 2).
Described next is an example of feedback as shown in Non-patent Document 1 with the aforementioned DRX considered. FIG. 13 contains a timing chart and sequence chart showing the flow of processing between the base station apparatus and mobile station apparatus in the conventional mobile communication system. DRX is shown in “912” in FIG. 13, and subframes 6 to 14 correspond to the duration (herein, referred to as Non-active Time) except the Active Time. As shown in “910”, resources of each kind of feedback information are allocated in subframes 1, 4, 7, 10, 13 and 16 as in the example of FIG. 11, and the base station apparatus sets the transmission signal number-of-sequence information to be transmitted at a frequency of once every four times in the allocated resources.
In other words, feedback is set to transmit the transmission signal number-of-sequence information in subframes 1 and 13 and the reception quality information and transmission signal preprocessing information in subframes 4, 7, 10 and 16. In addition, in order to halt feedback in accordance with the Non-active Time of DRX notified from the base station apparatus, feedback from the mobile station apparatus is given only in subframes 1, 14 and 16, and transmitted as feedback is the transmission signal number-of-sequence information (step S901), the reception quality information and transmission signal preprocessing information (step S902), and the reception quality information and transmission signal preprocessing information (step S903).
However, transmission of the number of transmission signal sequences in the subframe 13 corresponding to the subframe 16 (step S903) is in the Non-active Time, and there is the problem that the base station apparatus cannot know information that the reception quality information and transmission signal preprocessing information transmitted in the subframe 16 (step S903) corresponds to which number of transmission signal sequences. Non-patent Document 2 describes calculating and transmitting the reception quality information and transmission signal preprocessing information according to the last transmitted number of transmission signal sequences, but when the opportunity for DRX is large with respect to a rate of change in propagation path, the possibility is high that the number of transmission signal sequences is varied from the optimal number, and as a result, there is the fear of reducing throughput characteristics.
Further, as in the case of not transmitting the number of transmission signal sequences due to DRX, such a case arises that the number of transmission signal sequences cannot be transmitted because it is necessary to transmit another information with a higher priority at timing scheduled to transmit the number of transmission signal sequences.
[Non-patent Document 1] Summary of AH on AI 6.3.4 “UE Procedures for downlink shared channel”,
3GPP TSG-RAN WG1 Meeting #52, R1-081137
[Non-patent Document 2] 3GPP TS 36.321 V8.0.0 (2007-12) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) Medium Access Control (MAC) protocol specification (Release 8)